Journal of Oceanography

, Volume 68, Issue 4, pp 545–560 | Cite as

Resistance of Hong Kong waters to nutrient enrichment: assessment of the role of physical processes in reducing eutrophication

  • Jie Xu
  • Kedong Yin
  • Joseph H. W. Lee
  • Donald M. Anderson
  • Yuelu Jiang
  • Xiangcheng Yuan
  • Alvin Y. T. Ho
  • Paul J. Harrison
Original Article


Hong Kong waters receive high nutrient loading from year-round sewage effluent and Pearl River discharge during the summer wet season. We assessed the role of physical processes in reducing eutrophication by calculating a eutrophication reduction index for four different hydrographical areas and four seasons. We used outdoor incubation experiments to assess the response of phytoplankton when physical (mixing and dilution) processes and mesozooplankton grazing were reduced. The primary regulator of phytoplankton growth in low nutrient eastern waters (reference site) shifted from nutrients in the wet season to increased vertical mixing in the dry season. In the highly flushed western waters and Victoria Harbour, the majority (>86 %) of the eutrophication impacts were reduced by strong hydrodynamic mixing (turbulence, vertical mixing, and flushing effects) all year. In southern waters, eutrophication effects were severe (chlorophyll a of up to ~73 μg L−1) and was regulated by the ambient phosphate (PO4) concentration (~0.1 μM) during summer. In contrast, 62–96 % of the potential eutrophication impacts were reduced by physical processes during other seasons. Bioassays also revealed that the yield of chlorophyll from dissolved inorganic nitrogen (DIN) that was taken up by phytoplankton [1.1–3.3 g Chl (mol N)−1] was not significantly different in both N- and P-limited cases. In contrast, the uptake ratios of DIN:PO4 (26:1–105:1) and Chl:P ratios [42–150 g Chl (mol P)−1] in the P-limited cases were significantly (p < 0.05, t test) higher than the N-limited cases [~16DIN:1P and 22–48 g Chl (mol P)−1]. The C:Chl ratios ranged from 32 to 87 g g−1. These potential ranges in ratios need to be considered in future nutrient models.


Eutrophication impacts Hydrodynamics Algal biomass Pearl River discharge Sewage effluent Hong Kong Phosphorus limitation Chl:N, Chl:P, and C:Chl ratios 



Financial support for this research was provided by the University Grants Council of Hong Kong AoE project (AoE/P-04/04-4-II). We thank the Hong Kong Government EPD for the use their water quality monitoring data.


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Copyright information

© The Oceanographic Society of Japan and Springer 2012

Authors and Affiliations

  • Jie Xu
    • 1
  • Kedong Yin
    • 2
  • Joseph H. W. Lee
    • 3
  • Donald M. Anderson
    • 4
  • Yuelu Jiang
    • 1
  • Xiangcheng Yuan
    • 1
  • Alvin Y. T. Ho
    • 1
  • Paul J. Harrison
    • 1
  1. 1.Division of EnvironmentThe Hong Kong University of Science and TechnologyHong Kong SARPeople’s Republic of China
  2. 2.Australian Rivers InstituteGriffith UniversityBrisbaneAustralia
  3. 3.Department of Civil and Environmental EngineeringThe Hong Kong University of Science and TechnologyHong Kong SARPeople’s Republic of China
  4. 4.Biology DepartmentWoods Hole Oceanographic InstitutionWoods HoleUSA

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